Medicament delivery devices for automatic or semi-automatic injection of medicaments have been known for many years. While the first generations of injectors merely designed to deliver a medicament as quickly as possible, increased use of the devices by patients in non-clinical settings has led to the necessity of providing further handling and safety functions.
Important handling and safety functions of medicament delivery devices include inhibiting premature actuation of the device (misfiring). To ensure that the medicament is properly injected, actuation of the device is inhibited until the auto-injector is correctly positioned at a dose delivery site. Furthermore, since the member delivering the medicament can be sharp and may be contaminated after the device has been actuated, devices that retract or cover the medicament delivery member when the device is withdrawn from the dose delivery site have been developed. To prevent that a person unintentionally contacts the medicament delivery member and to allow safely discarding the device, some devices feature a mechanism that locks the device once the medicament delivery member is covered or retracted.
Another important feature with medicament delivery devices is to prevent the risk of using, or trying to use, devices that already have been used, i.e. ensuring that an intended user is provided with information regarding the status of the device, and also providing inhibiting features after use of a medicament delivery device. Many medicament delivery devices are arranged with some sort of actuation mechanism, often including a push button or the like. Such push buttons are often positioned at a distal end of the device, furthest away from a dose delivery site such that a finger, often a thumb, may operate the button when holding the device. Such an arrangement is disclosed in the document EP 850079, in which a so called pen injector is disclosed having a dose setting mechanism comprising a dose setting knob at a distal end of the device. When turning the dose setting knob a dose of medicament is set. In order to deliver the dose, the dose setting knob is pressed in the proximal direction into an end position where it is axially locked. When a subsequent dose is to be delivered, the dose setting knob is again rotated, whereby it is unlocked and moved in the distal direction.
The device according to EP 850079 is intended for multiple doses, and therefore the dose setting knob has to be returned to its initial position. Even though locked after dose delivery, it is easy to unlock the button for the subsequent dose. For a medicament delivery device that is intended for a single dose, it should not be possible to manipulate the device such that the dose button may be returned. A user might then get the impression that the device has not been used and may try to administer a dose with a used device. If the user does not have access to another medicament delivery device, he may unexpectedly find himself lacking delivery devices to fulfil a medication scheme.
As shown above, available medicament delivery devices either do not provide the necessary handling, safety and information functions or they require cooperation of one or several complex mechanisms. Accordingly, there is a need for medicament delivery devices that comprise mechanisms providing some or all of these functions in a reliable manner, with as few parts as possible. This is especially important for single-use devices, where low manufacturing cost is a necessity.